<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>js异步加载</title>
    <script src="./tools.js" ></script>
</head>
<body>
  defer 异步加载 只能在ie中使用 发生时刻 在页面解析完毕 <br>
  aysnc w3c标准 ie9以上 Google 火狐 <br>
</body>
</html>
<script type="text/javascript">
loadScript('tools.js',function(){
   console.log(type('string'))
})

</script>